Ununited accessory caudal glenoid ossification centre and associated joint mouse as a cause of lameness in a cat

CASE SUMMARY: A 16-year-old neutered female domestic shorthair cat was evaluated for chronic lameness of the right thoracic limb. On clinical examination, pain was localised to the right glenohumeral joint. Radiography and arthrography of the right glenohumeral joint revealed an ununited accessory caudal glenoid ossification centre, abbreviated here to ununited caudal glenoid (UCG), and a joint mouse. The UCG and attached joint mouse were removed via arthroscopy and this resulted in complete resolution of the clinical signs. The cat was euthanased 3 years later, for an unrelated cause, having shown no recurrence of lameness. RELEVANCE AND NOVEL INFORMATION: UCG should be considered as a differential diagnosis for cats with lameness of the thoracic limb. The clinical implications of a UCG have been described in dogs, but to our knowledge have not yet been described in cats. Excision of the UCG, as described in dogs, may be an effective treatment for this condition.